The typical asking rate per listing is in the $10's per square foot per year. The O'Fallon submarket is seeing a decrease in rates. In the last 3 months, the median rate fell $6 per sqft per year. That's a 24% decrease in rent.
In the last 90 days, 19 listings have been made available, which means spaces are probably going fast. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,250 sqft. Most properties in this area are around 1 stories. Most buildings in this region were built in 2001 and are Class A.